<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Overview</title>
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
<link rel="home" href="../../index.html" title="Chapter&#160;1.&#160;Fiber">
<link rel="up" href="../callbacks.html" title="Integrating Fibers with Asynchronous Callbacks">
<link rel="prev" href="../callbacks.html" title="Integrating Fibers with Asynchronous Callbacks">
<link rel="next" href="return_errorcode.html" title="Return Errorcode">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
<td align="center"><a href="../../../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="../callbacks.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../callbacks.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="return_errorcode.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="fiber.callbacks.overview"></a><a class="link" href="overview.html" title="Overview">Overview</a>
</h3></div></div></div>
<p>
        One of the primary benefits of <span class="bold"><strong>Boost.Fiber</strong></span>
        is the ability to use asynchronous operations for efficiency, while at the
        same time structuring the calling code <span class="emphasis"><em>as if</em></span> the operations
        were synchronous. Asynchronous operations provide completion notification
        in a variety of ways, but most involve a callback function of some kind.
        This section discusses tactics for interfacing <span class="bold"><strong>Boost.Fiber</strong></span>
        with an arbitrary async operation.
      </p>
<p>
        For purposes of illustration, consider the following hypothetical API:
      </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">AsyncAPI</span> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
    <span class="comment">// constructor acquires some resource that can be read and written</span>
    <span class="identifier">AsyncAPI</span><span class="special">();</span>

    <span class="comment">// callbacks accept an int error code; 0 == success</span>
    <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">errorcode</span><span class="special">;</span>

    <span class="comment">// write callback only needs to indicate success or failure</span>
    <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
    <span class="keyword">void</span> <span class="identifier">init_write</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">data</span><span class="special">,</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">callback</span><span class="special">);</span>

    <span class="comment">// read callback needs to accept both errorcode and data</span>
    <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Fn</span> <span class="special">&gt;</span>
    <span class="keyword">void</span> <span class="identifier">init_read</span><span class="special">(</span> <span class="identifier">Fn</span> <span class="special">&amp;&amp;</span> <span class="identifier">callback</span><span class="special">);</span>

    <span class="comment">// ... other operations ...</span>
<span class="special">};</span>
</pre>
<p>
      </p>
<p>
        The significant points about each of <code class="computeroutput"><span class="identifier">init_write</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">init_read</span><span class="special">()</span></code> are:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
            The <code class="computeroutput"><span class="identifier">AsyncAPI</span></code> method only
            initiates the operation. It returns immediately, while the requested
            operation is still pending.
          </li>
<li class="listitem">
            The method accepts a callback. When the operation completes, the callback
            is called with relevant parameters (error code, data if applicable).
          </li>
</ul></div>
<p>
        We would like to wrap these asynchronous methods in functions that appear
        synchronous by blocking the calling fiber until the operation completes.
        This lets us use the wrapper function&#8217;s return value to deliver relevant data.
      </p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top"><p>
          <a class="link" href="../synchronization/futures/promise.html#class_promise"><code class="computeroutput">promise&lt;&gt;</code></a> and <a class="link" href="../synchronization/futures/future.html#class_future"><code class="computeroutput">future&lt;&gt;</code></a> are your friends
          here.
        </p></td></tr>
</table></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2013 Oliver Kowalke<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="../callbacks.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../callbacks.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="return_errorcode.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
